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The cotton pulp is generally made by soda process, and the raw materials of cotton pulp
include waste cotton and linters of textile industry. The cotton pulp contains pure
cellulose, it has long and thin fiber, good tenacity, elasticity, and absorptivity. The cotton
pulp paper is fine and soft, usually has high opaqueness and also can be stored for a
long time. Bleached cotton pulp applies for text paper manufacture, such as filter paper,
drawing paper, security paper. The unbleached cotton pulp is used to manufacture
vulcanized paper and baby paper. Besides, the cotton pulp can be used as the raw
material of rayon, cellulose acetate.
About cotton fiber
As main raw material of cotton pulp, cotton linter refers to the short fiber that leaves on
the cottonseed hull. The cotton linter is shorter than lint cotton, but they have similar
maturity. Cotton linter has the higher content of cellulose, is the fiber materials for light
industry, military industry, chemical industry and medical industry. According to the
cotton ginning process, the cotton linter can be divided into three types and nine
classes.
The cotton linter has high content of cellulose and low content of lignin, the cotton pulp
is easy to bleach and hard to yellow. Chloride content of cotton pulp is low, and suitable
pentosan content decides the good water absorption of cotton fiber, the ash content is
high and can be removed by special methods. Maturity is a key indicator of cotton linter
quality, it has close connection with other indicators. The higher is the maturity, the
larger is the cellulose content, and the less is the non-cellulose impurities content.
Advantages of cotton fiber
Except for the high content of cellulose, low content of non-fibrous cell and long fibers,
the cotton fiber has other advantages as follows.
The crystallinity of cotton fiber is about 70%.
The thinner is cotton fiber, the better is hygroscopicity.
The bendability of cotton fibers, it is hard to break.
The heat resisting property of cotton fiber is the best among all natural fibers.
Cotton fiber has high beating degree, and it is long and even.
The natural bending of cotton fibers decides it has some good mechanical properties
like friction and cohesion.
Cotton pulp applications
Because the cotton pulp has different property with wood pulp, wheat straw pulp, it can
be applied to manufacture various kinds of paper, such as security paper, vulcanized
base paper, condenser paper, napkin, drafting paper, tracing paper and abrasion
resistant paper, etc.
Security paper
Security paper is used to print paper money, bond, and credentials. Security paper is
strong, durable and water-fast. Raw materials of security paper adopt chemical wood
pulp or bleached rag pulp. The cotton pulp for security paper is soft and thin, the high
cellulose content and lignin content of cotton pulp decide the high degree of whiteness
and durability of cotton pulp.
Vulcanized base paper
Vulcanized base paper is a kind of industrial and technical paper that is used as the
material of vulcanized fiber paper. The cotton pulp cellulose has high purity and low
content of non-fibrous impurity. Based on the processing, the vulcanized base paper
has high strength, evenness and absorptivity.
Cotton linter alkaline pulping process
Cotton linter alkaline pulping is the most common in the cotton pulp making. The main
process of cotton linter alkaline pulping can be generally divided into 5 procedures,
including material preparation, pulp cooking, pulp washing, pulp screening and
degritting, pulp bleaching and beating.
Material preparation
The cotton linter is treated before entering into paper and pulp mills. Open and break up
the treated cotton linter with cotton slitter, feed the cotton linter into carding machine
and remove the cotton seed hull and stalk and other impurities. The impurity rate of
treated cotton linter is between 1% and 3%, purifying rate is required above 85%.
Pulp cooking
The cotton linter was send into cyclone separator, white liquor is also added, and the
cotton linter is evenly dipped and sent into pulp digester. To reduce the temperature of
cellulose pulp and alkaline content, the cooked pulp should be sent into next step – pulp
washing process. The cotton pulp cooking is mainly used to improve wettability of cotton
fiber by removing the oil, fat, pectin, lignin and other impurities. As for the cotton pulping
equipment, rotary digester is typical in China, the pulp mills of USA, Japan usually
adopt continuous tubular digester.
Pulp washing
The cooked cotton pulp fiber is long, should be beated, or the pulp will affect the pulp
screening, bleaching process. Excepting for cutting the fibers, beating also increase the
hydration degree of cotton pulp fiber and wash the cotton pulp. Cotton pulp washing
equipment includes vacuum drum washer, twin roll press, single screw press, etc.
Pulp screening and degritting
Pulp screening process uses the hole of screen to separate fine pulp and coarse
screenings. For removing different impurities, the cotton pulp screening adopts
various screening equipment in series.
The pulp degritting clear the sand, metal debris and other impurities that produced by
cotton linter and pulp cooking process.
Pulp bleaching
After the pulp screening, cleaning, concentration, for improving the purity and whiteness
of cotton pulp, the virgin pulp can be bleached according to specific requirement.
Currently, most pulp mills adopt the hypochlorite bleaching, in order to prevent the
cotton pulp from damage, the bleaching agent, pulp consistency, pH value, bleaching
temperature and time should be strictly controlled.
Medium Consistency Mixer
Why Choose CNBM？
CNBM is a paper pulping machine manufacturer that provides paper pulp solution and
related pulp making equipment, such as pulp digester, blow tank, twin roll press,
vacuum drum washer, etc. We customize the pulp plants like wood pulp production
line, bamboo pulp production line, bagasse pulp production line, wheat straw pulp
production line, reed pulp production line, jute pulp production line, etc.
